New data from the Centers for Disease Control and Prevention show that birth rates among unmarried women in the U.S. between the ages of 35 and 39 shot up 48% between 2002 and 2012. For older women between 40 and 44 years old, this rate—while very low—rose 29% between 2007 and 2012.

That means for every 1,000 women 35 to 39 years old who are not married, there were 31 births in 2012, compared with 29 births in 2007 and 21 births in 2002. For unmarried women 40 to 44, this figure edged up from seven births in 2007 to nine births in 2012.

U.S. women are much more likely to have children out of wedlock than they used to. Roughly four in 10 U.S. births are to unmarried women, a figure that peaked in 2009 and hasn’t budged much since, according to the CDC.

The rise of the unmarried mom in America has stirred concern for years. Married parents tend to be more stable and have higher household incomes, which benefit children. And a gap is growing between America’s married parents, who tend to be better-educated and higher-earning, and unmarried parents, who are likelier to be less-educated and lower-earning. This so-called marriage divide could fuel social and economic inequality.

But the CDC’s latest findings show that trends related to unmarried moms vary greatly by age: It’s becoming much more common for middle-aged, unmarried women to have kids, as taboos ease. At the same time, younger women are delaying having children, to pursue career opportunities. Unwanted teen births, meanwhile, have plummeted, especially among black and Hispanic women.

The phenomenon of non-marital childbearing rose steadily in the 1980s and then sharply in the mid-2000s. The recession, which began in late 2007, along with progress reducing unwanted teen births, have recently pushed the numbers down slightly. Last year, there were 1.6 million births to unmarried women, down 7% from a peak of 1.7 million in 2008. This is still more than double the level of 1980, probably due to the increased social acceptance of having kids out of marriage.

The CDC’s data suggest the nature of non-marital childbearing is changing: Less and less does the stereotypical image of the single mother hold true. “Cohabiting unions,” where two unmarried people have a romantic relationship and live together, have increased, along with births within those unions. Between 2002 and the period from 2006-2010, the percentage of recent non-marital births within cohabiting unions jumped from 41% to 58%.

Some research shows measures of father involvement are very similar among married and cohabiting fathers. In other words, the increasing number and quality of cohabiting unions could mean the fabric of the American family—two parents, two incomes, raising children—isn’t fraying as much as some researchers long feared.

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